This work is a continuing study of events that occur preparatory to and at the time of fertilization. The peroxidative system activated at the time of fertilization, that is dependent upon release of an ovoperoxidase from cortical granules will be studied, with special attention to the mechanism of synthesis of hydrogen peroxide, the mechanism of action of the ovoperoxidase, and the role of the enzyme in the alteration of the glycocalyx and in prevention of polyspermy and the assembly of the fertilization membrane with specific incorporation of the ovoperoxidase. A linear sequence of events responsible for triggering will be further studied. Attention will be directed toward ion movements that accompany the reaction and their roles in different phases of the acrosome reaction.